Exercise is good for us — that’s one of the main themes of this blog, and one that I’m sure not many readers would dispute. But it can take a lot of time. Someone training for a marathon might easily spend more than 10 hours a week running, stretching, showering and so on. What is the opportunity cost of spending all that time? Justin Wolfers, an economist at UPenn’s Wharton School, did a somewhat tongue-in-cheek segment for NPR’s Marketplace analyzing the economics of running:

Runners World magazine recently argued that marathon running is an incredibly cheap sport. All you need is a pair of shoes, and you’re off and running. But they’re wrong.

You see, they were emphasizing the out-of-pocket cost, which is small. But the foundation of all economics is something called opportunity cost. It says that the true cost of something is the alternative you have to give up.

It’s an amusing piece, as well as a primer on some basic principles of economics like opportunity cost and the law of comparative advantage. But he makes a few asides that get the commenters riled up (see also Wolfers’ entry on the Freakonomics blog). And his analysis is (necessarily, I guess, given the space requirements) pretty simplistic. I think he could make a much stronger case for the mental and physical benefits of running that would yield real financial rewards. Fortunately, he still comes to the right conclusion: running is worth it!